Angiogenesis is a process involving the growth of new blood vessels from pre-existing vessels. In healthy adults, angiogenesis is quiescent in most of the organs, and is only present in limited circumstances such as the menstrual cycle. However, angiogenesis may occur in certain pathological conditions, such as during tumor growth, retinal disorders and wound healing. Studies have shown that angiogenesis plays an important role in the progression of tumors and development of retinal diseases. Inhibiting angiogenesis can be an effective treatment of many types of cancer. (Folkman, 2002, Role of Angiogenesis in Tumor Growth and Metastasis, Semin Oncol. 29 (6 Suppl 16): 15-8; Witmer et al., 2003, Vascular Endothelial Growth Factors and Angiogenesis in Eye Diseases, Prog Retin Eye Res. 22:1-29).
Angiogenesis is regulated by many factors. The vascular endothelial cell growth factor (VEGF) plays a critical role in angiogenesis (Leung et al., 1989, Vascular Endothelial Growth Factor Is a Secreted Angiogenic Mitogen, Science, 246: 1306-1309; Ferrara et al., 2003, The Biology of VEGF and Its Receptors, Nature Medicine 9: 669-676). VEGF is a polypeptide, secreted by multiple types of cells, and it is highly expressed in tumor cells. High levels of VEGF expression correlate to aggressiveness of tumors.
VEGF binds to specific receptors in the vascular endothelial cells, and initiates a series of signal transduction pathways that lead to the proliferation and migration of vascular endothelial cells. VEGF binds to two different receptors, that is, VEGFR1 and VEGFR2. VEGFR2 is the key receptor for VEGF signal transduction that triggers angiogenesis. (Neufeld et al., 1999, Vascular Endothelial Growth Factor (VEGF) and its Receptors, The FASEB Journal, 13:9-22).
VEGFR2 consists of the extracellular domain, the transmembrane domain and the intracellular domain. VEGF binds to the extracellular domain of VEGFR2. The binding leads to the autophosphoration of tyrosine kinase in the intracellular domain, which as a result initiates signal transduction, resulting in vascular endothelial cell proliferation, migration, and vessel formation. In addition, VEGFR2-mediated signal transduction inhibits the apoptosis of vascular endothelial cells.
Given the key role of VEGFR2 in the signal transduction for angiogenesis, it is possible to inhibit angiogenesis, thus treat diseases, by blocking the binding of VEGF to VEGFR2. Therefore, pharmaceutical agents blocking the VEGFR2 pathway are capable of treating many angiogenesis-related diseases, such as cancers and AMD.
Monoclonal antibodies (mAb) have become a new class of therapeutic agent due to their ability to bind with high specificity to a target, their long plasma half-life, and their low toxicity/side effects. Furthermore, recent progress in humanized or full human antibody technologies have helped to avoid the early problems associated with murine antibodies, including immunogenicity in vivo. Therefore, monoclonal antibodies have become an attractive option for pharmaceutical compositions.
The human body has millions of lymphocytes, secreting various antibodies. Each lymphocyte secretes only one type of mAb specific to a single epitope. Therefore, each human has a huge number of mAbs. Antibodies that are secreted in different persons may vary due to various antigens exposed to the individuals. In some persons, in response to specific physiological and pathological conditions, antibodies that bind to the person's own proteins are produced.
Human mAbs can be generated by isolating lymphocytes secreting specific antibodies. In addition, human mAbs can also be generated by other methods, such as by screening human antibody phage-display library or immunizing transgenic mice that carry human antibody genes.
Chinese Patent No. 00805856.3 discloses a human immunoglobulin molecule, including its amino acid sequences, which binds to and neutralizes VEGFR2. Currently, no mAb containing the amino acid sequence identical or similar to the subject invention has been disclosed for the inhibition of angiogenesis and the treatment of vascular diseases.